The present invention relates to a motor control system for a sewing machine in which thyristors are employed for motor driving control. More particulary, the invention relates to a one stitch sewing control system for a sewing machine in which thyristors are employed for motor driving control.
A conventional motor control system for one stitch sewing, in which the motor is energized by selection of the one stitch sewing mode and downward force on the foot controller and stops after execution of the one stitch sewing operation, employs either a mechanical control means such as a one way clutch and stopper, or an electric control circuit which controls energization and deenergization of the motor in accordance with the movement of the sewing needle. The mechanical control means correctly controls the one stitch sewing. However, it has many mechanical components and produces mechanical impact shock and noise. Therefore it may be worn out after a relatively short life. Energization and deenergization of the motor by an electric circuit for one stitch sewing control also has some defects; stop control is relatively rough in high speed one stitch sewing, and motor speed should be low to stop the sewing needle correctly at a predetermined halt position after completion of a stitch.